A controllable oscillator circuit of this type is known for example, from U.S. Pat. No. 3,936,773.
The cascade circuit of the two sections is regeneratively fed back from the output to the input for the frequency at which there is unity gain in the loop formed by the first and second sections and the feedback, with a phase shift of 90.degree. in each of the two sections. To this end each of the two sections, hereinafter also referred to as quadrature sections, of the known oscillator circuit comprises an integrator and an analog multiplier.
For each frequency within a given frequency range the integrator realises a 90.degree. phase shift, while the loop gain for a desired frequency within the last-mentioned frequency range is controlled at unity by means of said analog multiplier of each of the two quadrature sections. Since this frequency range determines the oscillator control range and is in itself comparatively narrow (in practice the integrators realise an accurate 90.degree. phase shift only for some frequencies), the known oscillator circuit comprises a phase correction circuit in which a part of the output signal of one of the two quadrature sections is added to its input signal, which part is controllable in amplitude by means of the amplitude detection arrangement. Although this results in a given increase of the oscillator control range, it appears in practice that the control range of the known oscillator circuit is limited at its upper side to a maximum value of the order of 100 kHz. Furthermore, unwanted large deviations in the phase quadrature relation between the two phase quadrature oscillator signals are not prevented by means of said phase correction circuit. Moreover, comparatively large time constants are required for low oscillation frequencies in the known oscillator. To realise such large time constants in integrated circuits, a comparatively large chip surface is required so that the known oscillator, particularly for low oscillation frequencies, is less suitable for integration.